The invention relates to bore hole drills in which shaped cutters are included as preforms of bonded abrasive particles or as relatively large bodies of ceramics such as boron carbide, silicon carbide, titanium carbide and natural abrasives such as carbonados. The shaped cutters are of a size and shape of a different order of magnitude than diamonds, employed in prior art diamond drills. This difference creates a problem arising from the geometry of the drill and space consideration.
The problems of a suitable distribution of the shaped cutters in order that the cutters traverse the entire face of the bore hole which is being cut by the bit is aggravated by the requirements of the bit hydraulics.
As is well known in this art, the drilling fluid which is introduced through passageways in the bit is designed to cool the bit, wash the cutting elements so that they present a clean cutting face, move the cutting to the gage of the bit and lift them up the annulus between the drill string and the wall of the hole.
In order that the drilling fluid have this function, it must have a desirably high mass velocity through the drill bit nozzles without requiring an undesirable high back pressure.
These various requirements have been particularly difficult to meet where the bit is destined for operation in relatively soft formations where clogging of the bit is appreciable. It is also a problem in harder formations.